Tetrafluoroethylene/hexafluoropropylene copolymers with higher drawability

ABSTRACT

A tetrafluoroethylene/hexafluoropropylene copolymer with high drawability is provided. Also provided is a process employing the polymer and an article coated with the polymer.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. Ser. No. 09/492,021,filed Jan. 26, 2000, now allowed, the disclosure of which is hereinincorporated by reference, which claims priority from U.S. Ser. No.60/117,780 filed Jan. 29, 1999.

FIELD OF THE INVENTION

[0002] The invention relates to melt-processable tetrafluoroethylene(TFE)/hexafluoropropylene (HFP) copolymer melt pellets having animproved processability for wire and cable application and to a methodof using this polymer to coat wire and cable conductors.

BACKGROUND

[0003] Melt processable copolymers with TFE and HFP are well known underthe name FEP. As perfluorinated thermoplasts, such copolymers haveunique end-use properties like chemical resistance, weather resistance,low flammability thermal stability and outstanding electricalproperties. Like other thermoplasts, FEP is easily molded to coatedwires, tubes, pipes, foils and films.

[0004] Because it has excellent thermal stability and is practicallynon-flammable, FEP is frequently used for plenum constructions to meetfire resistance requirements. It is also the natural choice in datatransmission cables due to its excellent dielectric properties. See EP 0423 995 A1.

[0005] High processing speeds are desired when wires and cables areextrusion coated. Such high extrusion rates are limited by theoccurrence of melt-fracture like with many thermoplasts. Melt-fractureresults in surface roughness and/or uneven wall thickness. To increasethe extrusion speed the molecular weight distribution of the usedcopolymer is believed to be very broad as disclosed, for example, inU.S. Pat. No. 4,552,925 for FEP.

[0006] For substantially broadening of the molecular weightdistribution, the copolymer is mostly used as a mixture of at least twoFEP's with largely differing molecular weights. The molecular weightsare often characterized by the melt viscosity or the melt flow index(MFI-value). The desired mixtures are often produced by polymerizing thecomponents separately and mixing them in form of the latices, reactorbeads or fluff before melt pelletizing. Thus the manufacturing of thesemixtures is a cumbersome and costly process.

[0007] Other FEP-mixtures are disclosed in DE 2,613,642 and DE2,613,795.

[0008] These mixtures were claimed to be advantageous for diminishingthe foaming during the stabilization process of FEP. This process iscarried out by treating the resin at high temperatures up to 400° C.preferably in presence of water vapour. By this process the thermallyunstable endgroups, mostly COOH and CONH₂ groups (easily detected byIR-spectroscopy), are removed.

[0009] These mixtures have a very broad molecular weight distributionwhich according to conventional wisdom, results in an improvedextrudability.

[0010] Removal of thermally unstable end-groups is required for theprocessing of FEP, in particular for wire-coatings. The decompositionreaction of the unstable endgroups, described in Modern Fluoropolymers,Ed. John Scheirs, Wiley & Sons 1997, p. 228 leads to bubbles and holesin the end-articles. Melt pelletizing of unstabilized polymer resinsresults in corrosion of the equipment used in the process and in metalcontamination of the melt pellets. However, the stabilization process ofDE 2,613,642 and DE 2,613,795 is very difficult to manage due tocorrosion of the equipment because of the use of a water steam.

[0011] Metal contaminants are difficult to cope with. Such metalcontaminants may result in degradation and decomposition of thecopolymer at high processing temperatures. Decomposition generally leadsto discoloration and degradation, and to a build up of die drools. Diedrools are accumulations of molecular fractions of the polymer at thesurface of the die exit. Die drools impair the coating processing. Also,cone breaks can occur.

[0012] During the process of coating a wire, the molten polymer isextruded as a tube or sheath and drawn by vacuum onto the wire. Conebreaks are the discontinuities or breaks that occur during this process.Every time a cone break occurs, the coating process has to bere-initiated and one must wait for the system to reach equilibrium. Thuslong processing times are more difficult to achieve. Productivity isdiminished.

[0013] Furthermore, extrusion temperatures have to be kept as low aspossible to counteract the decomposition reactions and resulting toxicoff-gases, the rate of which substantially increases with elevatedtemperatures. On the other hand, lower extrusion temperatures result inhigher melt-viscosities and thus an earlier onset of the melt fracture.Lowering the intrinsic melt viscosity by lowering the molecular weightresults in poorer mechanical properties.

[0014] As a result, the material should be made more thermally stablenot only by eliminating the thermally unstable endgroups but also byavoiding metal contaminants and Mw fractions which are more prone toshear and/or thermal degradation.

[0015] Another way to eliminate unstable endgroups is postfluorinationas disclosed in, for example, GB 1 210 794, U.S. Pat. No. 4,743, 658 andEP 0 457 255 B1. Generally, elemental fluorine diluted with nitrogen isused at elevated temperatures up to close to the onset of melting of thepolymer. The polymer may be subjected to fluorination in form of meltpellets, agglomerates or fluff. Here, too, excessive metal contaminationshould be avoided.

[0016] EP 0 222 945 B1 discloses the fluorination of hardenedagglomerates, there called granules.

[0017] The fluorination leads to perfluorinated endgroups whereas thehumid heat treatment as mentioned above, mechanistically cannot resultin a fully fluorinated polymer resin. It is believed that inserteddouble bonds are present in the backbone leading to an inherent thermalunstability. These kinds of bonds may lead to a discoloration at longexposures to high temperatures.

[0018] There is another degradation reaction of FEP disclosed in U.S.Pat. No. 4,626,587. The onset of this reaction is supposed to occur bysplitting the HFP diads in the middle of the chain at temperatures abovethe melting point. Such diads are formed at the radical polymerizationby recoinbination of the correspondent polymer radicals as a terminationstep. The destruction of the diads at processing conditions leads tohalving the molecular weight of these polymer chains and hence tonegatively affecting the mechanical properties, and to formation of moreunstable endgroups. As U.S. Pat. No. 4,626,587 teaches, such diads aredestroyed by subjecting the material to very high shear rates attemperatures far above the melting point. This process also is verycostly.

[0019] There is another process disclosed in EP 0 789 038 A1 to reducethe backbone instability. The process is disclosed to use relativelylarge amounts of a chain transfer agent to suppress termination ofpolymer radicals by recombination.

SUMMARY OF THE INVENTION

[0020] The invention provides a material for wire and cable coatingswhich can be processed at higher speeds and at higher temperatures forlonger run times of the equipment. The invention furthermore provides amanufacturing process which is more economical and better controllableas to quality consistency. Still further, the invention provides aprocess for reducing die drool and the frequency of cone breaks duringwire and or cable coating extrusion coating.

DETAILED DESCRIPTION

[0021] The polymer according to the invention comprises a copolymer ofTFE and HFP. It has a HFP content in the range of 5 to 22 weight % (w%), preferably between 10 to 18 w %, a TFE content of between 95 to 78wt %, preferably between 90 to 82 wt %, and optionally up to 3 mnol % ofa fluorinated monomer copolymerizable with HFP and TFE. The optionalcomonomer is preferably a perfluoroalkylvinylether as is disclosed in EP0 789 038 and DE 2 710 501 C2. The monomer content is measured viaIR-spectroscopy as described in US 4,552,925. The polymers of theinvention typically have a melting point between 240-275° C., preferably245-265° C.

[0022] The polymer of the invention is essentially free of thermallyunstable endgroups which are removed via postfluorination of theagglomerates. Essentially free of endgroups means less than 80 endgroupsper million carbon atoms, preferably less than 40 endgroups and mostpreferably less than 30 endgroups per million carbon atoms. The materialis essentially of high purity grade as to metals; that is the totalamount of iron, chromium, nickel is less than 200 parts per billion(ppb), preferably less than 100 ppb.

[0023] The polymer of the invention used to coat wire and cableconductors has a very narrow molecular-weight distribution, i.e., aratio of Mw to Mn of less than about 2 (Mw=weight average, Mn =numberaverage molecular weight). This ratio may be as low as 1.5. This is incontrast to FEP-grades recommended for wire coatings with highextrudation rates where a broad molecular weight distribution isrecommended. The broadness of the molecular weight distribution ismeasured according to a method published by W. H. Tuminello in Polym.Eng. Sci 26, 1339 (1986). For high speed wire extrusion the MFI of thepolymer is ≧15. Lower MFI's are useful for other applications such asfoamed coaxial cable. This polymer is preferably essentially free ofunstable endgroups. It most preferably is the polymer of the invention.

[0024] A melt pelletized copolymer according to the invention with aMFI-value of 24 and containing 15 w % HFP may be manufactured asdescribed below. This polymer can be extruded with a wire coatingextruder at, for example, 390° C. (735° F.) at a rate of 1500 feet/minover a run time of the equipment of 6 hours without exhibitingdiscoloration and without producing substantial amounts of die droolsand with fewer cone-breaks in contrast to commercial FEP grades. Thesurprisingly good performance is not fully understood.

[0025] Despite a narrow molecular weight distribution high processingrates can be achieved. As has been discussed above, the art teaches thata broad molecular weight distribution is needed to achieve such highprocessing rates. It has now been discovered that a narrow molecularweight distribution performs better, thus overcoming a well establishedprejudice.

[0026] Furthermore, discoloration does not occur during processing. Thisis an indication of the absence of a decomposition reaction. TheMFI-value of the extruded material practically does not change. Theamount of IR-detectable endgroups does not increase. Both observationsindicate that there is no significant chain degradation. Thisobservation suggests that weak backbone linkages as HFP-diads (U.S. Pat.No. 4,626,587) are not present in the material.

[0027] The non-occurrence of discoloration together with theseobservations, namely the nearly unchanged MFI-value and the nearlyunchanged amount of endgroups is evidence of the absence of asignificant decomposition reaction even at higher processingtemperatures. It is believed that this results in reduced die drools andthe much reduced frequency of cone breaks. Hence, the copolymeraccording to the invention exhibits a surprisingly high thermalstability even under shear. As a result, the polymer of the inventioncan beneficially be used in other applications.

[0028] The evidence of the absence of a decomposition reaction issurprising and not fully understood. It is believed that metalcontaminants, in particular heavy metals like Fe, Ni, Cr might induce adecomposition reaction. Indeed, the used material contained only lessthan 50 ppb of Fe+Ni+Cr ions as measured by neutron activation analysis.Thus the material according to the invention can be called a high puritygrade.

[0029] The polymer of the invention may be made by the manufacturingprocess as described below.

[0030] The polymerization may be carried out in form of a radicalaqueous emulsion polymerization as it is known in the art, (see U.S.Pat. No. 2,946,763). Ammonium or potassium persulfate may be used asinitiators. As emulsifiers standard emulsifier like the ammonium salt ofperfluoro-octanoic acid may be used. Buffers like NH₃, (NH₄)₂CO₃ orNaHCO₃ can be incorporated in the recipe. Typical chain transfer agentslike H₂, lower alkanes, methylene fluoride or methylene chloride can beused. Chloride and bromine containing chain transfer agent should beavoided. These components may cause strong corrosion at the fluorinationprocess. Polymerization temperatures can range from 40-120° C.,preferably 50-80° C.; polymerization pressures may range from 8-25 bar,preferably 10-20 bar. HFP is precharged and fed into the reactoraccording to the rules of copolymerization. (See for example, ModernFluoropolymers, ed. John Scheirs, Wiley & Sons, 1997, p. 241). Thepreferred version of the polymerization recipe here is an alkali metalsalt-free recipe.

[0031] Furthermore, it is preferred to carry out the copolymerisationwithout any chain transfer agents in contrast to EP 0 789 038 A1. Chaintransfer agents intrinsically broaden the molecular weight distribution.The polymerization rate/time curves should have the shape as publishedin Modern Fluoropolymers, Ed. by Johns Scheirs, Wiley & Sons, 1997 p.226. As hinted to in this paper, the Mw/Mn ratio can be easilycalculated from the rate/time curves in absence of a chain transferagent via eq. (6), p 230 and assuming that termination solely occurs viarecombination. Recombination leads to a Mw/Mn ratio of 1.5 for smallconversions. Termination primarily via chain transfer results in a Mw/Mnratio of 2.

[0032] The radical polymerization also can be carried out in a nonaqueous medium, like R 113, as disclosed in U.S. Pat. No. 3,528,954. Thenon aqueous process is not preferred because it is believed to alsogenerate smaller amounts of high molecular weights due to the gel effectin this “suspension” polymerization. Weak back bone linkages (HFP-diads)are more likely to be generated by the gel effect. The occurrence of agel effect at the aqueous emulsion polymerization is most unlikely tooccur because propagation and termination take place on the surface ofthe latex particles.

[0033] The dispersion obtained from the polymerization is preferablymechanically coagulated with a homogenizer (see EP 0 591 888 B1) andagglomerated with a water immiscible organic liquid like gasoline, atechnique well known in the art (see Modern Fluoropolymers, ed. by J.Scheirs, Wiley & Sons, 1997, p. 227). The agglomerates are free flowingspherical beads with a diameter of 0.5-2 mm. The free flowability ispreferred for the technical reliability of carrying out the subsequentwork up steps. The agglomerate is dried by first purging with nitrogenand then under moderate vacuum at temperatures up to 180° C.

[0034] Chemical coagulation may also be employed. However, it isgenerally done with acids.

[0035] This is not preferred as it results in very high levels of metalcontaminants at all subsequent work up steps.

[0036] The agglomerate may then be fluorinated at temperatures between60-150° C., preferably at 100-140° C. with a mixture of fluorine innitrogen. The mixture generally contains 10 w/% fluorine. Fluorinationcontinues until at least 90-95% of the endgroups of the originalagglomerate are eliminated. Higher fluorination temperatures can resultin a difficultly controllable change of the MFI-value which can be up to30%. This can result in a broadening of the molecular weightdistribution and negatively effect performance. As a result,reproducibility is not achieved, thus negatively affecting quality andconsistency of wires and cables coated with the polymer. Reaction timeswere not observed to be discernibly shortened by higher temperatures;thus higher fluorinating temperatures are not considered to beadvantageous. Moreover higher temperatures can lead to presintering oreven sintering of the agglomerate can cause a sticking of the materialto the walls of the equipment. The fluorination is carried out in atumble drier to keep the material in motion. Thus more homogeneousreaction conditions are achieved. The free flowable agglomerate has tobe free of fines and mechanically stable enough to avoid producing toomany fines at the after treatment. Fines may impair the reliability ofoperating the process. Hardening of the agglomerate as disclosed in EP 0222 945 B1 is not required.

[0037] The fluorination of the agglomerate has two advantages. It is nota diffusion controlled reaction since the endgroups reside on thesurface of the latex particles. Reaction times therefore are relativelyshort. Next the friable, not hardened agglomerate is soft enough to notscratch off metal contaminants from the wall of the tumble drier. Thusthe level of metal contaminants is reduced. Both features do not holdfor the fluorination of melt pellets. In this case the fluorinationprocess requires higher temperatures and much longer reaction times tomake allowance to the diffusion control of the reaction. Furthermore,the hard and sharp melt pellets scratch off a considerable amount ofmetal from the wall of the tumble drier. Increasing reaction timesresult in higher metal contamination. This contamination is difficult toremove. The level of metal contamination was observed to increase by upto 2 orders of magnitudes when the pellet process was used.

[0038] The fluorinated agglomerate is subsequently melt pelletized.

[0039] The agglomerate suffers from some disintegration during thedrying and fluorination processes. Fines are produced resulting inuneven free flowing behaviour of the material. It is advantageous tocompact the fluorinated agglomerate before melt pelletizing. Thus a morereliably constant feeding rate is achieved.

[0040] Melt pelletizing fluorinated agglomerates provides manyadvantages compared to the melt pelletizing of non fluorinatedagglomerates. Melt pelletizing occurs practically without decomposition.The MFI-value practically stays unchanged. This observation suggests theessential absence of weak backbone linkages. The corrosion of theequipment is substantially reduced. The pick up of metal contaminationthus is insignificant. The emission of gaseous decomposition chemicalsat the die exit is significantly reduced (e.g., by 4 orders ofmagnitudes). Thus the whole process is safer to operate. Die drools aresubstantially reduced. Thus the process needs less attention. The colorof the melt pellets does not exhibit any discoloration in contrast tothe melt pellets originating from non fluorinated agglomerates which mayleave the extruder. These nonfluorinated pellets are typically “coffeebrown” in color.

[0041] The MFI value of the melt pellets manufactured via the describedprocess is observed to only slightly increase by about 10% compared tothe MFI value of the resil as polymerized. Thus quality consistency canbe achieved more easily.

[0042] As described in DE 195 47 909 A1 the melt pellets aresubsequently subjected to an aqueous treatment to remove the volatilesand COF-groups. Here too, the near-absence of gaseous decompositionchemicals and acidic endgroups reduce the corrosion of the stainlesssteel water treatment vessel considerably. Thus further heavy metalcontamination is diminished. Furthermore, water soluble saltsoriginating from the manufacturing process are removed. The amount ofextractable fluoride ions is greatly diminished to less than 1 ppm.

[0043] Test Methods

[0044] The MFI value is measured according to ASTM D 1238 (DIN 53735) at372° C. with a load of 5 kg. The MFI value can be converted to the valueof the melt viscosity in 0.1 Pas (Poise) by dividing 53150 by the MFIvalue (g/min).

[0045] The HFP content is measured via FTIR-spectroscopy as disclosed inU.S. Pat. No. 4,552,925. The absorbances at the wave-numbers of 980 cm⁻¹and 2350 cm⁻¹, respectively, are measured with a film of 0.05±0.01 mm inthickness which is formed at 350° C. with a FTIR-Nicolet Magna 560 FTIRspectrometer. The HFP content is calculated according to the followingequation

HFP content (w %)=A ₉₈₀ /A ₂₃₅₀×3.2.

[0046] The endgroups, —COOH, —COF, CONH₂, are determined via FTIRspectroscopy as disclosed in EP 226,668 B1 and U.S. Pat. No. 3,085,083.A film of a thickness of 0.1 mm which is formed at 350° C. is usedtogether with a reference film of a material known to have none of theendgroups to be analyzed. A FTIR-Nicolet Magna 560 spectrometer was usedusing the interactive subtraction mode of the software. When thepopulation of endgroups are reported herein, the sum of isolated andassociated COOH-groups, CONH₂ and COF-groups are meant.

[0047] Melting points of the copolymers were determined by DSC by themethod of ASTM D-4591-87 at a heating rate of 10 K/min. The reportedmelting temperature is the peak temperature of the endotherm on the2^(nd) melting.

[0048] The broadness of the molecular weight distribution characterizedby the Mw/Mn ratio was measured via rheological spectroscopy with anAdvanced Rheometer Expansion System (ARES) supplied by RheometricScientific. Measurements were carried out at 372° C. and evaluatedaccording to W. H. Tuminello, Polyin. Eng. Sci., 26, 1339 (1986).

[0049] Metal contents were measured by extracting the samples with 3%HNO₃ for 72 hours at room temperature and subjecting the extract toatomic absorption spectroscopy.

[0050] The extractable fluoride ion content of the melt pellets wasmeasured as disclosed in EP 0 220 910 B1. However, extraction wasperformed only with water.

EXAMPLE 1

[0051] A stainless steel 1500 l reactor was charged with 1000 l ofdeionized water containing 3 kg of the ainmonium salt ofperfluoro-octanoic acid. Air was removed by evacuation and purging withN₂. The reactor was heated to 70° C. and the temperature kept constant.2 kg of 25% ammonia in water was added.

[0052] The vessel was pressurized with TFE and HFP to 17 bar such thatthe partial pressure of HFP was 12.5 bar. The polymerization was startedby adding 1600 g of ammonium persulfate diluted in 5 l deionized waterwithin 10 min. The pressure was kept constant by feeding a gaseousmixture of TFE/HFP into the reactor. The TFE/HFP weight ratio was 0.14.After 6 hours the reaction is stopped by interrupting the monomer feed.The monomers were vented off. The reactor was cooled to room temperatureand discharged. The solid content of the polymer dispersion was 29%, thedispersion was practically free of coagulum. The MFI-value was 20 g/min.The HFP content of the copolymer was 13 w/%. The melting point was 255°C. The copolymer had 660 COOH endgroups per 10⁶ carbon atoms. Mw/Mn wasmeasured to 1.7. A Mw/Mn value of 1.6 was calculated from thepolymerization rate time curve.

[0053] The dispersion was coagulated with a hoinogenizator andagglomerated with gasoline. The agglomerate was washed three times withdeionized water and dried for 6 hours at I80° C. in a tumble drier firstby purging with nitrogen and then under vacuum.

[0054] The resulting agglomerate was divided into 2 parts. One part wassubsequently melt-pelletized, water treated and dried. It had a coffeebrown color. It was then fluorinated and again water treated to removeresidual COF-endgroups. The discoloration disappeared. This sample iscalled A0. The material had 43 endgroups per million carbon atoms. Theother part of the agglomerates was first fluorinated, melt pelletizedand treated with water and dried. This sample is called A1 and had 18endgroups per million carbon atoms.

[0055] At each processing step the content of iron, nickel and chromiumwas measured via the extraction method. Table 1 shows the resultstogether with the amount of endgroups. TABLE 1 Metal contaminations forsamples AO and A1, respectively, after the various work up steps.Agglomerate had 660 endgroups. Sample A0: Fluorination of the MeltPellets (Comparison) Work Up Steps metal water treated content meltWater fluorinated melt pellets [ppb] agglomerate pellets treated meltpellets endproduct*⁾ Fe 10 247 198 892 550 Ni >10 41 22 56 21 Cr >10 3819 71 27 Sample A1: Fluorination of the Agglomerate (Invention) Work UpSteps water treated metal content fluorinated Melt melt pellets [ppb]agglomerate agglomerate pellets endproduct*⁾ Fe 10 14 18 14Ni >5 >5 >5 >5 Cr >5 >5 >5 >5

[0056] The fluorination was carried out in a 300 l stainless steeltumble drier with a mixture of 10% fluorine in nitrogen at 140° C. forsample A0 and at 100-140° C. for sample A1, restively. Details are givenin Table 2. The fluorine mixture had to be replaced several times, socalled refills. At the end of the reaction excess fluorine was removedby blowing air through the reactor. Excess fluorine was adsorbed bypassing the air stream through a bed of Al₂O₃ granules and through awasher containing an aqueous slurry of CaCO₃. TABLE 2 FluorinationConditions for Samples A0 and A1, respectively. reaction overallfinal**⁾ temp. Number*⁾ reaction time number of sample material form °C. of refills [h] endgroups AO Melt pellets 200 16 8.5 43 A1 Agglomerate140 7 4 12

[0057] Water treatment (see DE 195 47 909 A1) was carried out in a 1000l stainless steel reactor. 200 kg of melt pellets and 400 1 deionizedwater containing 1125% aqueous ammonia were charged into the reactor.The reactor was heated Up to 100° C. and kept at this temperature for 4hours for the nonfluorinated melt pellets and for 1 hour for thefluorinated melt pellets. These reaction times were required to bringthe COF endgroups below 5 ppm. The reactor was cooled by replacing thewater 2 times. Drying was achieved by blowing hot air through thereactor. The melt pellets had an extractable fluoride ion content of 0.1ppm.

EXAMPLE 2

[0058] Sample A11 was run through a wire coating extruder under twodifferent sets of conditions together with a commercial productdesignated C1. Sample A11 was manufactured like A1 but had a MFI valueof 24 g/min. A11 is a reproduction of A1 as to the polymerization andwork up. It had 28 endgroups and an iron content of 18 ppb. The Mw/Mnratio was measured to be 1.6. The calculated value was 1.7. Theextractable fluoride ion content was 0.2 ppm.

[0059] The coating conditions are listed in Tab. 3. TABLE 3 CoatingPerformance of the material according to the invention in comparison toa commercial product C1 and to sample A0 Run # 1 2 3 Sample A11 A11 C1MFI g/min 24 24 21 Copper Wire temp. (F.) 350 380 350 176° C. 193° C.177° C. Cone Length (inch) 2.0 1.5 2.0 Die Temperature (F.) 716 735 716380° C. 391° C. 380° C. Extruder Speed (rpm) 21.3 24.7 18.5 Line Speed(fpm) 1710 2006 1402 521 mps 611 mps 427 mps

[0060] Temperature profiles, not given in the tab., were slightlyadjusted to maximize the line output while maintaining the deviation ofthe insulation eccentricity between 0.0003 and 0.0007 inches.

[0061] Runs 1-2 did not show noticeable die drools and no cone-breaksduring the run time. Run 3 showed significant die drool and cone-breaksduring equivalent run time. When C1 was aged above its melt temperature(i.e., about 250° C. it showed a noticeable brownish discoloration.

EXAMPLE 3

[0062] Samples A11, A12 and a commercial products were run through aslightly different wire-coating extruder.

[0063] The coating conditions are listed in Tab. 4 TABLE 4 CoatingPerformance of the material according to the invention in comparison to2 commercial products Run # 1 2 Sample A11/A12 C2 MFI g/min 24/23 25Copper wire temp. (F.) 380/375 350 193° C./190° C. 177° C. Cone Length(inch) 2.0 2.0 5.1 cm 5.1 cm Die temp. (F.) 760 760 404° C. 404° C.Extruder Speed (rpm) 42.5 32.0 Line Speed (fpm) 1700 1390 518 mps 415mps/417 mps

[0064] Temperature profiles were adjusted to maximize the line outputwhile maintaining the deviation of the insulation eccentricity between0.0003 and 0.0007 inches (0.00076 and 0.0018 cm).

[0065] Run #1 did not show noticeable die drool and exhibited only 2cone-breaks during a period of 29 hours of extruding wire colors ofblue, green, orange, brown and white.

[0066] Run #2 showed considerable die drool and averaged 6-8 cone-breaksduring a run period of 24 hours.

What is claimed:
 1. A process for reducing the frequency of cone breaksduring a wire coating extrusion process comprising the steps of: (a)providing a copolymer derived from 78 to 95 w/% of tetrafluoroethylene,5 to 22 w/% hexafluoropropylene, and optionally up to 3 mol % of afluorinated monomer copolymerizable with tetrafluoroethylene andhexafluoropropylene wherein the ratio of Mw to Mn is less than 2; (b)providing a wire or cable conductor; (c) extruding the copolymer aroundthe conductor at a temperature sufficient to produce a steady flow ofthe polymer.
 2. A process according to claim 1 wherein the polymer hasless than 80 unstable end groups per 1×10⁶ carbon atoms.
 3. A processaccording to claim 1 wherein the polymer has less than 200 ppb of heavymetals.